This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-076583, filed Mar. 19, 1999, the entire contents of which are incorporated herein by reference.
The present invention mainly relates to an optical signal receiver apparatus and, more particularly, to an optical signal receiver apparatus including, as discrete components, a photo-detector such as a photodiode and an integrated circuit having at least an amplifier.
An optical signal receiver apparatus having the function of receiving a transmitted photo-signal and converting it into an electric signal is indispensable for an optical communication system. An optical signal receiver apparatus capable of high speed communication uses a PIN photodiode as a photo-detector, converts a photoelectric current (signal current) from the PIN photodiode into a voltage signal by using a transimpedance amplifier, and outputs the signal.
In such an optical signal receiver apparatus, the PIN photodiode and transimpedance amplifier are manufactured in different processes. The former is manufactured as an element chip, and the latter is manufactured as an integrated circuit. These two components are electrically connected through bonding wires.
As the transmission rate of an optical communication system is increased for high speed communication, an improvement in high-frequency transmission characteristics is required to broaden the transmission band. If the transmission band is broadened to several GHz, bonding wires, which pose no problem in a low-frequency range, produce an adverse effect. With this adverse effect, the high-frequency transmission characteristics deteriorate. That is, bonding wires serve as inductances in a high-frequency range.
In a conventional optical signal receiver apparatus, the power source line of a photodiode as a photo-detector is much longer than the signal line of the photodiode. For this reason, if a photo-signal transmission band is as wide as several GHz, the band is limited, resulting in a decrease in gain in a high-frequency range, in particular.
It is an object of the present invention to provide an optical signal receiver apparatus which can sufficiently shorten not only the signal line of a photo-detector but also its power source line, and can properly receive a wideband photo-signal like a signal in a GHz band.
It is another object of the present invention to provide an optical signal receiver apparatus which can realize stable operation even at the time of reception of a high-level photo-signal.
According to the present invention, there is provided an optical signal receiver apparatus comprising a photo-detector configured to convert a photo-signal into an electric signal, an integrated circuit incorporating an amplifier which amplifies the electric signal, and a power source supply section which supplies a power source current to the photo-detector through the integrated circuit.
With this arrangement, for example, the signal terminal and power source terminal of the photo-detector can be directly connected to the integrated circuit with boding wires. This makes it possible to sufficiently shorten the power source line of the photo-detector as well as the signal line of the photo-detector which extends to the amplifier in the integrated circuit. Therefore, when a photo-signal in a wide band is to be received, a band is not cut off up to a high frequency. This can realize proper receiving operation while making the most of the element characteristics of the photo-detector such as a PIN photodiode.
In addition, in the present invention, the integrated circuit incorporates a current detector which is inserted in a power source supply path to the photo-detector to detect a power source current flowing into the photo-detector by utilizing the operation of supplying a power source current to the photo-detector through the integrated circuit. Various control operations can therefore be performed by using the detection results obtained by this current detector.
For example, this apparatus includes a current drain circuit which compares a predetermined reference voltage with a voltage corresponding to the power source current detected by the current detector, and drains a DC current from the input side of the amplifier when the voltage corresponding to the power source current is equal to or higher than the reference voltage. This makes it possible to prevent any unnecessary DC current from flowing into the amplifier at the time of reception of a high-level photo-signal and realize stable operation of the amplifier.
More specifically, the current detector is formed from a resistor and designed to convert a power source current flowing into the photo-detector into a voltage whose peak voltage is almost equal to twice a forward voltage drop at a p-n junction or Schottky junction and output the voltage.
The current drain circuit comprises a first level shift circuit constituted by a plurality of series-connected p-n junction elements or Schottky junction elements to obtain the reference voltage, and a second level shift circuit constituted by a plurality of series-connected p-n junction elements or Schottky junction elements to obtain a voltage corresponding to the power source current by level-shifting an output voltage from the photo-detector. The p-n junction elements or Schottky junction elements constituting the second level shift circuit are fewer than the p-n junction elements or Schottky junction elements constituting the first level shift circuit by one. With this arrangement, since the relationship in magnitude between the reference voltage and the voltage corresponding to the power source current detected by the current detector changes depending on whether a photoelectric current is output from the photo-detector, a DC current can be drained on the input side of the amplifier when a photoelectric current flows.
According to the invention, there is provided an optical signal receiver apparatus comprising: a module substrate; a photo-detector mounted on said module substrate to convert a photo-signal into an electric signal; an integrated circuit chip mounted on said module substrate to be juxtaposed with said photo-detector and incorporates an amplifier configured to amplify the electric signal; a bonding wire connecting said photo-detector to said integrated circuit chip; a power source terminal mounted on said substrate to be near said integrated circuit chip and connected to an external power source; and a bonding wire connecting said power source terminal to said integrated circuit chip to supply a power source current from said external power source to said photo-detector through said integrated circuit chip.